There is known already from French patent application 2 682 072 an obturator of this kind that includes a cap provided with a peripheral rim that comes to face the metal sheet at the border of the opening when the obturator is placed in it. A wall whose external surface has a shape corresponding to that of the opening is connected transversely to the peripheral rim. A number of lugs project from this wall, extending it. At the end of each lug a snap-fastening blade extends between an attachment end where it is connected to the lugs and a free end, parallel to the peripheral rim. Each snap-fastening blade has on the outside an insertion cant that is sloped as far as a step.
French patent application 2 707 233 also describes an obturator having the above features which further includes a fin disposed on the step of each snap-fastening blade and the exterior surface of which forms a gripping counter-cant.
The openings for which these obturators are provided are generally produced in the metal sheet by punching, and often have a rough peripheral border. It therefore often happens that the portions of this border in contact with the insertion cants dig into the blades instead of sliding over them and causing them to bend.